Run a separate ground to the body of the solenoid to see if that helps ? Then check the little wire for 12 volt signal when you push the button .
Then short the 2 big posts to each other and see what happens .

I have a Kaw that was making the 02 size cable jump apart when I pushed the button , looked funky as hell . Turns out the solenoid was fine but the starter was shorted direct to ground . I also use a 1000cca battery for testing stuff or wiring my bikes , it shows the mistakes pretty quick !! Good luck .